1. Field of the Invention
The present invention relates to a network system and a line concentrator for constructing the network system,
2. Description of the Prior Art
A shared media type of network has hitherto been adopted as a basic structure in a prior art network system, e.g., in a LAN (Local Area Network) system represented by Ethernet. That is, there is adopted a construction for receiving and transferring data by use of communication lines for connecting a plurality of terminal equipments to each other. Therefore, the terminal equipments connected to the same LAN share a bandwidth with each other. Accordingly, when a traffic volume increases, the bandwidths of the communication lines come to deficiency enough to cause such a case that the smooth transmission and receipt of the data might be hindered. One of countermeasures against this problem may be a network system using a line concentrator (e.g. switching HUB).
FIG. 31 is a block diagram illustrating a whole configuration of the network system employing a line concentrator 1. Referring to FIG. 31, a plurality of terminal equipments (hereinafter simply called xe2x80x9cterminalsxe2x80x9d) 2a-2d are connected via communication lines to the line concentrator 1. The data is transferred and received based on packet communications between the respective terminals 2a-2d. A packet used at this time is stored with a data-transmitted-side address and a data-transmitting-side address in addition to the data to be transmitted.
Therefore, the respective terminals 2a-2d have network addresses (IP addresses (Internet Protocol addresses): layer 3 addresses) of the respective terminals 2a-2d, and MAC (Media Access Control) addresses. Then, when one of the terminals 2a-2d transmits the data to other terminal, the transmitting terminal generates the packet. This packet is stored with the data-transmitted MAC address and the data-transmitting network address, and the data.
On the other hand, the line concentrator 1 incorporates, as illustrated in FIG. 31, a MAC address table 3 stored with the MAC addresses of the terminals 2a-2d. When the line concentrator 1 receives the packet from one of the terminals 2a-2d, the data-transmitted MAC address stored in the packet is compared with the MAC address stored in the MAC address table 3, whereby the data-transmitted MAC address is confirmed, and the packet transmitting terminal and the packet transmitted terminal are brought into such a state as to be connected to each other via one communication line.
For example, referring again to FIG. 31, in the case of transmitting the data packet from the terminal 2a to the terminal 2c, when the line concentrator 1 receives the packet transmitted by the terminal 2a, the terminal 2a is connected via the one communication line to the terminal 2c with the MAC address of the terminal 2c that is stored in that packet (see the broken line in FIG. 31). This is known as a port switching function.
With this port switching function, a medium (communication line) is occupied between the terminal 2a and the terminal 2c, and, besides, the bandwidth is also occupied. Thus, the line concentrator 1 enables the terminals 2a-2d to transfer and receive the data through the one-to-one communication. Hence, the data can be smoothly transferred and received.
In contrast with this, there must be a case wherein each of the terminals 2a-2d transmits the data to the plurality of terminals. In this case, each of the terminals 2a-2d is stored with an address (a broadcast address) purporting that the packet should be transmitted to all the terminals, in an area for storing the packet data-transmitted MAC address. The packet stored with the broadcast designation as the transmitted address is termed a broadcast packet.
This broadcast packet is, when received in the line concentrator 1, transmitted to the plurality of terminals in accordance with setting of the line concentrator 1. More specifically, the line concentrator 1 is capable of unifying the plurality of communication lines (an interface accommodating the communication lines) connected to itself by setting, into a single or a plurality of groups. The line concentrator 1, upon receiving the broadcast packet, distinguishes which group the communication line accepting the transmission of the broadcast packet belongs to, and sends the broadcast packet to the communication line belonging to that group. Herein, a group having such a domain that the line concentrator 1 transmits the broadcast packet is referred to as a broadcast domain.
For example, as shown in a block diagram of FIG. 32, if all the communication lines connected to the line concentrator 1 are set as one broadcast domain, and when the line concentrator 1 receives the broadcast packet transmitted from, e.g., the terminal 2a, the communication lines for connecting the terminals 2a-2d to the line concentrator 1 are connected to each other (see the broken line in FIG. 32), and the broadcast packet is thereby transmitted from the line concentrator 1 to the terminals 2b-2d. 
By the way, as illustrated in FIG. 33, there may be a case where a terminal 2e is newly connected via the communication line to the line concentrator 1 in the network system shown in FIG. 31. The terminal 2e immediately after being connected is in such a state as to possess the network address at all.
In anticipation of such a case, as illustrated in FIG. 33, an address possession server 4 (hereinafter simply termed a xe2x80x9cserverxe2x80x9d) is connected via the communication line to the line concentrator 1 in the network system. Herein, the server 4 possesses a self network address (hereinafter called a xe2x80x9cserver addressxe2x80x9d) and a single or a plurality of an unused network address. This server 4, upon receiving a supply request of the network address from the terminal, supplies the unused network address possessed by the server 4 itself.
Given hereinbelow is an explanation of a process when the server supplies the network address to the terminal 2e in FIG. 33. A premise is that the line concentrator 1 is set to transmit, upon receiving the broadcast packet, this broadcast packet to all the terminals 2a-2e and the server 4 that are connected to the line concentrator 1.
At first, the terminal 2e transmits a broadcast packet (xe2x80x9caddress possession server_DISCOVER packetxe2x80x9d hereinafter called a xe2x80x9cDISCOVER packetxe2x80x9d) in which the data is a supply request for the server address and the unused network address. The reason why the xe2x80x9cDISCOVER packetxe2x80x9d is defined as the broadcast packet is that the terminal 2e immediately after being connected to the network system is in such a state that a position (address) of the server 4 is unknown. The terminals 2a-2d and the server 4 receive this xe2x80x9cDISCOVER packetxe2x80x9d via the line concentrator 1.
Next, when the server 4 receives the xe2x80x9cDISCOVER packetxe2x80x9d, there is transmitted a broadcast packet (xe2x80x9caddress possession server_xe2x80x9cOFFER packetxe2x80x9d: hereinafter called an xe2x80x9cOFFER packetxe2x80x9d) in which the data consists of the server address of the server 4 and a single or a plurality of unused network addresses. The reason why the xe2x80x9cOFFER packetxe2x80x9d is defined as the broadcast packet is that the terminal 2e is in such a state as to have no self address, and therefore the server 4 is impossible of specifying the terminal to which the xe2x80x9cOFFER packetxe2x80x9d should be transmitted from the xe2x80x9cDISCOVER packetxe2x80x9d. The terminals 2a-2e receive this xe2x80x9cOFFER packetxe2x80x9d via the line concentrator 1.
Next, when the terminal 2e receives the xe2x80x9cOFFER packetxe2x80x9d, the terminal 2e selectively obtains one network address from the single or the plurality of unused network addresses, and a broadcast packet (xe2x80x9caddress possession server_REQUEST packetxe2x80x9d: hereinafter called a xe2x80x9cREQUEST packet) in which the obtained result serves as a piece of data, is transmitted. This xe2x80x9cREQUEST packetxe2x80x9d is, as in the case of the xe2x80x9cDISCOVER packetxe2x80x9d, transmitted via the line concentrator 1 to the terminals 2a-2d and the server 4.
Next, the server 4, upon receiving the xe2x80x9cREQUEST packetxe2x80x9d, analyzes a content of the xe2x80x9cREQUEST packetxe2x80x9d and grasps which network address the terminal 2e obtained. Thereupon, the server 4 transmits a broadcast packet (xe2x80x9caddress possession server_ACK packetxe2x80x9d: hereinafter called an xe2x80x9cACK packetxe2x80x9d) in which the data is an acceptance acknowledgement of a result of the terminal 2e having obtained the network address. This xe2x80x9cACK packetxe2x80x9d is received by the terminals 2a-2e via the line concentrator 1.
If a plurality of network systems shown in FIG. 31 are provided, as illustrated in, e.g., FIG. 34, the respective line concentrators 1a, 1b are connected to routers 30 via the communication lines in each network system. Then, the network system as shown in FIG. 31 constitutes a segment.
The relay system 30 incorporates a so-called xe2x80x9crouting agent functionxe2x80x9d. With this routing agent functionxe2x80x9d, the relay system 30, when receiving the packet from one of the line concentrators 1a, 1b, transmits the packet to the other line concentrator 1a or 1b without any change in terms of content of the same packet.
For instance, referring to FIG. 34, if the terminal 2e immediately after being connected to the line concentrator 1a transmits the above xe2x80x9cDISCOVER packetxe2x80x9d to the server 4a and the server 4b as well, the xe2x80x9cDISCOVER packetxe2x80x9d is, when received by the line concentrator 1a, transmitted to all the communication lines connected to this line concentrator 1a. The xe2x80x9cDISCOVER packetxe2x80x9d is thereby transmitted to the server 3a and the terminals 2a, 2b, and also transmitted to the relay system 30 via the communication line on a backbone side. The relay system 30, upon receiving the xe2x80x9cDISCOVER packetxe2x80x9d, transmits the packet to the line concentrator 1b without changing the content of the xe2x80x9cDISCOVER packetxe2x80x9d by dint of the above xe2x80x9crouting agent functionxe2x80x9d. The xe2x80x9cDISCOVER packetxe2x80x9d is, when received by the line concentrator 1b, transmitted to all the communication lines connected to the line concentrator 1b. The xe2x80x9cDISCOVER packetxe2x80x9d is thereby received by the terminals 2c, 2d and the server 4b. The servers 4a, 4b are thus notified of the network address supply request of the terminal 2e, and subsequently the above-mentioned process is executed, whereby the terminal 2e obtains the self network address.
There arise, however, the following problems inherent in the prior art network system described above. That is, in the network system shown in FIG. 34, the packet switching for obtaining the network address is all performed by use of, as explained above, the broadcast packet between the terminal 2e and the server 4.
Accordingly, in the line concentrator 1, the terminals 2a-2e and the server 4 are connected to each other via the communication lines in order to transmit the broadcast packets to all the broadcast domains, and it follows that the packets such as the xe2x80x9cDISCOVER packetxe2x80x9d and the xe2x80x9cOFFER packetxe2x80x9d are transmitted to the terminals 2a-2d requiring no receipt of these packets. Consequently, the bandwidth shrinks, and the throughput decreases. Particularly when the data are transferred and received between the terminals enough to require a considerable network performance as in a file transfer, etc., there must be a large influence due to the reduction in the bandwidth. As explained above, a first problem is that smoothing of the data communications between the terminals is hindered.
By the way, the terminals 2a-2e in the network system shown in FIG. 34, if not possessed of the network address and the MAC address, are incapable of performing the communications between the terminals based on the one-to-one communication. Accordingly, the terminal 2e illustrated in FIG. 34 is still in such a state as to be incapable of performing the one-to-one communication with other terminals 2a-2d simply by obtaining the network address from the server 4.
For this reason, if the terminal 2e shown in FIG. 34 tries to transmit the data to, e.g., the terminal 2d, the terminals 2e must obtain the MAC address of the terminal 2d through ARP (Address Resolution Protocol). More specifically, the terminal 2e transmits an ARP packet (ARP request packet) to the terminal 2d and, at the same time, receives an ARP (ARP response packet) from the terminal 2d. The ARP request packet is, however, also defined as a broadcast packet. Hence, the first problem described above arises.
Further, the relay system 30, upon receiving the broadcast packet, transmits the broadcast packet to all the line concentrators connected to the router itself through the xe2x80x9crouting agent functionxe2x80x9d. It might be probable that the bandwidth is reduced, and the throughput decreases. Thus, even if each of the line concentrators 1a-1c incorporates the function to occupy the bandwidth of the communication line, there exists a second problem in which the data are not smoothly transferred and received between the segments in the case of the relay system 30 incorporating no function to occupy the bandwidth of the communication line.
Moreover, if the plurality of relay systems are employed in the network system, it may happen that the router transmits a control broadcast packet (e.g., RIP (Routing Information Protocol), etc. (hereinafter termed an xe2x80x9cinternal control packetxe2x80x9d) for controlling other routers and the line concentrators. In this case, it follows that the internal control packet is transmitted to each broadcast domain via each of the line concentrators 1a-1c. The internal control packet is, however, unnecessary for the respective terminals 2a-2e, whereby the above first problems is caused. Further, the internal control packet might contain confidential items of data such as basic construction data of the network system, and therefore a second problem arises, wherein the security of the network may be spoiled.
It is a first object of the present invention, which was contrived in view of the first and second problems given above, to provide a network system and a line concentrator that are capable of smoothly transferring and receiving by preventing a decreases in throughput due to a reduction in bandwidths.
It is a second object of the present invention, which was contrived in view of the third problem given above, to provide a network system and a line concentrator that are capable of keeping a confidentiality of information.
The following is a first construction of the network system of the present invention, which was contrived to obviate the problems described above. That is, a network system according to the present invention comprises a plurality of terminal equipments, a server, and a line concentrator to which the plurality of terminal equipments and the address possession server are connected via communication lines. The terminal equipment includes an address supply requesting element for, when possessing no self network address, transmitting an address supply request broadcast packet to the line concentrator. The line concentrator includes a plurality of interfaces, a first line data storing element for storing data about the interface receiving the address broadcast packet transmitted from the server, and a communication line control element for, when one of the plurality of interfaces receives the address supply request broadcast packet from one of the plurality of terminal equipments, reading the data about the interface receiving the address broadcast packet from the first line data memory storing element, and then transmitting the address supply request broadcast packet from only the relevant interface. The server includes a network address storing element for storing an unused network address in the network system, and an address supplying element for, when receiving the address supply request broadcast packet, transmitting the address broadcast packet containing the unused network address stored in the network address storing element.
The line concentrator may further include an address requesting element for generating the address supply request broadcast packet and transmitting the same packet to the server. The first line data storing element is thereby stored with the data about the interface receiving the address broadcast packet transmitted by the server in response to the address supply request broadcast packet. As a matter of course, the data about the interface may be inputted to the first line data storing element from outside. Further, the line concentrator may include a second line data storing element for, when one of the plurality of interfaces receives the address supply request broadcast packet, storing data about the interface receiving the address supply request broadcast packet. The communication line control element of the line concentrator, when one of the plurality of interfaces receives the address broadcast packet from the server, may read the data about the interface receiving the address supply request broadcast packet stored in the second line data storing element, and may transmit the address broadcast packet from only the relevant interface. Moreover, the line concentrator may further comprise a fiducial traffic volume memory table stored with a fiducial traffic volume, and a traffic measuring element for measuring a traffic volume per unit time and comparing this measured result with the fiducial traffic volume. The address requesting element, when the traffic measuring element detects a traffic volume less than the fiducial traffic volume, may generate the address supply request broadcast packet, and may transmit the same packet to the server. Furthermore, the line concentrator may further comprise a timer for measuring a predetermined time. The traffic measuring element may measure a traffic volume per unit time when the timer measures the predetermined time, and may compare this measured result with the fiducial traffic volume. In addition, the line concentrator may further comprise a procedure stopping element for generating a procedure stop broadcast packet for stopping packet switching for obtaining the unused broadcast packet between the plurality of terminal equipments and the server, and transmitting the same packet to the server.
According to a first construction of the network system of the present invention, the network address storing element of the server is stored with a network address of the server itself, and the address supplying element of the server, when receiving the address request broadcast packet, transmits an address broadcast packet containing the unused network address stored in the network address storing element and the network address of the server itself. In this case, the line concentrator may include an address storing element for storing the network address of the server itself, an address managing element for, when one of the plurality of interfaces receives the address supply request broadcast packet from one of the plurality of terminal equipments, reads the network address of the server itself that is stored in the address storing element, and a packet generating element for generating the address supply request packet in which a packet-transmitted address of the address supply request broadcast packet received by one of the plurality of interfaces is changed into the network address of the server itself that is read by the address managing element, and for transmitting the same packet to the server.
Further, the network address of the server itself may be inputted to the address storing element from outside, and, when the line concentrator receives the address broadcast packet, the address managing element may store the address storing element with the network address of the server itself that is contained in the address broadcast packet.
According to a second construction of the network system of the present invention, a network system comprises a plurality of terminal equipments, a plurality of line concentrators to which the plurality of terminal equipments are connected via communication lines, and a relay system to which the plurality of line concentrators are connected via the communication lines. The relay system includes a control packet transmitting element for transmitting a control broadcast packet of the relay system itself and/or the plurality of line concentrators. Each of the line concentrator includes a plurality of interfaces, a packet distinguishing element for, when one of the plurality of interfaces receives the packet from the relay system, determining whether or not the packet received from the relay system is the control broadcast packet, and a communication line control element for, when the packet distinguishing element determines that the packet received from the relay system is the control broadcast packet, making the control broadcast packet untransmissible from the plurality of interfaces.
According to a third construction of the network. system of the present invention, a network system comprises a plurality of terminal equipments, a plurality of first line concentrators to which the plurality of terminal equipments are connected via communication lines, and a second line concentrator to which the first line concentrators are connected via the communication lines. The plurality of terminal equipments include ARP requesting elements for, when having no data-transmitted MAC (Media Access Control) address, transmitting ARP (Address Resolution Protocol) request packets containing data-transmitted network addresses of the first line concentrators. The plurality of first line concentrators include first address converting elements for, when receiving the ARP request packet from one of the plurality of terminal equipments, transmitting, to the second line concentrators, the ARP request packet in which the packet-transmitted address of the received ARP request packet is converted into the address of the second line concentrator. The second line concentrator include a first address corresponding table stored with the network address in the network system in such a form as to correspond to the MAC address, and a responding element for, when receiving the ARP request packet from one of the plurality of first line concentrators, reading from the first address corresponding table the data-transmitted MAC address corresponding to the data-transmitted network address contained in the ARP request packet, for generating an ARP response packet containing the data-transmitted MAC address, and for transmitting the ARP response packet to the first line concentrator transmitting the ARP request packet.
According to a fourth construction of the network system of the present invention, a network system comprises a plurality of terminal equipments, a plurality of first line concentrators to which the plurality of terminal equipments are connected via communication lines, and a second line concentrator to which the first line concentrators are connected via the communication lines. The plurality of terminal equipments include ARP requesting elements for, when having no data-transmitted MAC (Media Access Control) addresses, transmitting ARP (Address Resolution Protocol) request packets containing data-transmitted network addresses of the first line concentrators. The plurality of first line concentrators include first address converting elements for, when receiving the ARP request packet from one of the plurality of terminal equipments, transmitting, to the second line concentrators, the ARP request packet in which the packet-transmitted address of the received ARP request packet is converted into the address of the second line concentrator, and a second address converting element for, when receiving the ARP request packet from the second line concentrator, transmitting to the plurality of terminal equipments the ARP request packet in which the packet-transmitted address of the ARP packet is converted into a broadcast designation. The second line concentrator includes a second address corresponding table stored with the network addresses in the network system in such a form as to correspond to the MAC addresses of the plurality of first line concentrators, and a third address converting element for, when receiving the ARP request packet from one of the plurality of first line concentrators, reading from the second address corresponding table the MAC address of the first line concentrator that corresponds to the data-transmitted network address contained in the ARP request packet, for generating an ARP request packet in which the MAC address of the first line concentrators serves as transmission destination addresses, and for transmitting the ARP request packets to the relevant first line concentrators.
According to the third and fourth constructions of the network system of the present invention, a network system may comprise a plurality of terminal equipments, a plurality of first line concentrators to which the plurality of terminal equipments are connected via communication lines, a second line concentrator to which the first line concentrators are connected via the communication lines, and an address resolution server to which the second line concentrator is connected via the communication line.
According to the network system of the present invention, it is possible to prevent a throughput from being decreased due to a reduction in terms of bandwidths for the communication lines for connecting the plurality of terminal equipments, the server and the line concentrator and also to properly transmit the data between the terminal equipments.
Further, in such a case that the network system is equipped with the relay system, the control broadcast packet is inhibited from being transmitted to the terminal equipments by providing the line concentrator with a packet distinguishing element. Therefore, the confidentiality of the data contained in the control broadcast packet can be kept, and, in turn, the confidentiality of information in the network system can be also held.